Hi Jason -
We just finished our yearly hydrant inspections here (and are moving on to our ARV Inspections); while I can't give pointers on Workforce (we're in the beta but unfortunately I haven't had to time to test it out and get all my other work done 😕 ), I think I can shed some light on the question you're asking.
I had a conversation with ESRI support regarding this at one point and as far as I understand it, right now there is no way to call data from your feature service into your related table. This was counter-intuitive to me that this was not available because two objects stored in the same place that are already talking to one another through a relationship -SHOULD- be able to pull data from one into the other. In our case, I wanted to pull our internal Hydrant ID numbers from the feature service into the related Hydrant Management Table so that when I viewed the related records, I could tell within AGOL which hydrants required repairs. We used GlobalIDs and GUIDs to create the relationship rather than based on the Hydrant ID numbers to avoid any relationship issues. In order to work around this, our operators were required to copy the ID # from the basemap labels I included in our custom basemap into new management records so we could quickly find records related to hydrants needing repairs as they came in from the field. The only way to both see related records easily and edit them was to dual-wield AGOL via desktop and Collector via tablet so you can immediately see related data and edit it. Other than these crude work arounds, the only way to see the related records is to download your data from AGOL and perform a "Make Query Table" in ArcGIS Desktop (only way to join the two tables with a 1:M relationship). However when you have thousands of features in a feature service, and occasionally multiple records for each feature, this download can take a while ... quite often in the business of emergency assistance infrastructure like a fire hydrant, this is a lot longer than questions requiring immediate attention can be left unanswered.
IMO, part of the problem here is that when you click on a feature in a feature service within AGOL, it doesn't offer you the ability to see the related records associated with that point in the primary pop-up. In order to see that instantly, you must also have collector open in front of you. While I did find that filtering the features and related table by edit date I could narrow down the data I had to sort through, this was imperfect (due to user error such as forgetting to re-symbolize hydrants from requiring inspection to complete or requiring maintenance/repairs, or accidentally moving our hydrant points around while editing).
Hope this helps.
